The primary goals of this project are analysis of the controls of gene expression and viral replication of human retroviral genomes and study of the functions of their individual gene products. Over the past year, our studies have focused primarily on the molecular biology of the AIDS retrovirus (RV) although a few studies on human endogenous retroviral DNA segments have continued. Previously, we had defined the major classes of AIDS RV RNA species detected in infected cells. To more clearly define the nature of the transcripts capable of encoding the A open reading frame, we have isolated a cDNA clone derived from the 5.0 kb viral mRNA species. This clone is capable of directing the synthesis of a 23 kD "A" protein in vitro. Furthermore, the A gene product appears to be important for replication as deletion of this region from an infectious proviral clone diminishes the infectivity of that DNA. The function of different gene regions of the AIDS RV is being analyzed by insertion of these gene regions into eukaryotic expression vectors. The AIDS RV tat gene has been inserted into MuLV and SV-40 based vectors, the A cDNA into an SV40 vector, and the env gene is currently being placed into amphotropic MuLV. In addition, a cDNA clone for CD4, the AIDS RV receptor, has been cloned in an MuLV based expression system and will be used to study the mechanism of AIDS RV infection of human cell lines. In efforts to identify homologues of the AIDS RV in normal human cells, we have detected the presence of several DNA species in normal human DNA that hybridize to the tat region of the AIDS RV under low stringency hybridization conditions. These DNA sequences will be molecularly cloned and analyzed to determine their relationship to the AIDS RV.